This invention is concerned with operator units for fire doors having a resettable fail-safe release mechanism.
Release mechanisms for roll type fire doors are well known in the art. Release mechanisms presently in use incorporate both a fusible link in series with a chain connected to the closing mechanism of the door, and an electromechanical arrangement responsive to a signal from a fire detecting device in series with said chain. Melting of either the fusible link or activation of the electromechanical arrangement by an alarm signal or power failure will release the chain thereby activating the closing mechanism of the door. U.S. Pat. No. 3,955,840 (Rawls et. al.) describes a door release mechanism that operates using this principle. Furthermore, the invention of Rawls et. al. can be used in the fail-safe mode, whereby the absence of electrical power (which often precedes a fire) will cause the fire door to close. Fail-safe operation is therefore the preferred mode for fire door release mechanisms.
The problem with these and similar mechanisms is that they need to be manually reset after activation. A heavy unpowered door must be raised, the chain rerouted and manually reconnected. This process takes about 20 minutes for most doors and requires experienced factory personnel to meet insurance company requirements. Nuisance activation of fail-safe systems caused by electrical outages is bothersome and expensive because manual resetting is needed every time there is an electrical outage. Several manufacturers have put time delays of up to 60 seconds into the system so that brief outages will not trigger false alarms. Although this minimizes the number of false alarms, it does not affect the cost nor time of reset. Furthermore a time delay of over a few seconds in fire door systems is dangerous because it defeats the purpose of quick door closing in response to alarm system signals.
The National Fire Protection Association (NFPA) specification NFPA 80 1990 edition titled "Standard for Fire Doors and Windows" added a requirement (section 15-2.4.3) which states, among other things, that rolling fire doors must be ". . . tested annually to check for proper operation and full closure." This must be done and adds considerable time and expense per door tested. Some insurance company regulations require biannual testing of fire doors in factories that they insure. Every time a door of the present art is fully tested in accordance with NFPA 80, the above described manual resetting process must be performed.
Patent application Ser. No. 859,833, filed on Mar. 30, 1992 and titled "A Mechanism for Controlling the Raising and Lowering of a Door" (Tsung-Wen Shea, inventor) discloses a mechanism for regulating the speed of descent of a closing fire door while allowing normal operation of the door during non-emergency conditions. The problem with Tsung's invention is that it is not fail-safe; electric power must be applied for an external alarm system to activate the relay to close the door. During a fire which disables the electricity, only heat activating the fusible link, will close the door.
What is needed is a fail-safe fire door release mechanism that can be reset simply should there be an outage, or during periodic requirements to test the door and the release mechanism.